1. Field of the Invention
The present invention relates to an external additive for an electrostatically charged latent image developing toner which is used to develop an electrostatically charged latent image in electrophotography, electrostatic recording, and the like, and particularly it relates to an external additive for a toner with a small particle size used for obtaining images of high quality.
2. Description of the Prior Arts
Dry developers used in electrophotography and so forth are generally classified into a one-component developer which consist of a toner prepared by dispersing a coloring agent in a binding resin and a two-component developer consisting of the toner and a carrier. In using these developers in copying operation, the developers are required to have good flowability, anti-caking property, fixing property, electrification property, and cleaning properties so as to be adapted to the process. In order to improve especially the flowability, anti-caking property, fixing property, and cleaning properties, inorganic fine particles are frequently added to the toner.
However, the dispersibility of the inorganic fine particles affect toner properties. Non-uniform dispersion of a toner may not give desired flowability, anti-caking property or fixing property, or may result in insufficient cleaning property, causing adhesion of the toner on a photoreceptor and image defect in black spots. For the purpose of improvement at to these problems, the use of inorganic fine particles having been surface-treated to make the surfaces thereof hydrophobic in Japanese Laying-open Publication Nos. 46-5782, 48-47345 and 48-47346.
However, when an organic photoreceptor or a toner with a smaller particle size is used to improve image quality, the use of the inorganic fine particles does not give sufficient performance. The organic photoreceptor has a softer surfaces and a higher reactivity than inorganic photoreceptor; therefore, the life of the organic photoreceptor is liable to become shorter. Such an organic photoreceptor is liable to change in quality or to be scraped at its surface. When a toner with a smaller particle size is used, the toner is low in flowability as compared to toners with a conventional particle size. Therefore, the amount of inorganic particles has to be increased, and thereby the inorganic fine particles may have caused the toner to adhere to the photoreceptor.